Late to the thread, and I'm going to switch from examining which 'person' is most important at the table to which 'role'.
So, in games that have roles of GM and player, the distribution of authorities and constraints differs on the game. In D&D, the GM has broad authority over almost every aspect of the game and few constraints, while the player has limited authority (general, only over their character in build and action declaration) and many constraints. Play is clearly centered around the GM.
In a Powered by the Apocalypse game, say Blades in the Dark, the GM has much more limited authority, now only over position and effect and scene framing (but constrained by player input) and many more constraints on authority. The players have much more authority and fewer constraints than in D&D. Everyone, though is under tighter constrained in regards to genre and setting than in D&D. Depending on the immediate need in the game, the more important role shifts between player and GM. For instance, when determining the score, the GM has no say, it's all the players (constrained by genre and setting) and the GM must accept the player's input and cannot violate it in scene framing or resolutions. So, here, the roles have shifted and play is less clearly GM centered than in D&D, as authorities alternate.
I don't think it's worthwhile to try to determine who the most important role at the table is, because you must have all roles present to have the game. Further, importance of role can vary greatly by the game, and even by the specific moment in the game.
I think a lot of thought is tied up into what we do in these roles, that are our choices, or are pushed by the game structure, without considering an outside view. It's easy to think that, since you do the prep and make the calls and play D&D that you can conflate you, the person, with the role of GM. The role of GM is pointless without the players -- it's neither more or less important in structure. In the social space, though, the level of work necessary to GM in the traditional D&D style (which you don't really have to do, it's more the traditions and assumptions built up around the game rather than an actual requirement to play) means that there are fewer people willing to do it, and fewer still who do it well, which leads to the assumption that the GM is the most important person. In reality, the GM is just more scarce, not more important. They are more valuable due to their scarcity rather than anything inherent to the role. And, this is borne out by the desire to protect the scarcity of the GM through gatekeeping -- you MUST do these things to be a GM and it's HARD to do well, so therefore there are FEWER people capable of being a GM. But, this is gatekeeping, pure and simple. You do not have to do the many things listed in this thread as 'needed' to GM, as some have noted to strong pushback. You can do it a lot simpler, if you change your assumptions and traditions about what a game looks like, even for stalwarts like D&D.